Borrelia burgdorferi, the Lyme disease spirochete, circulates between an Ixodes tick vector and a mammalian host, primarily Peromyscus leucopus mouse, in nature. The organism must migrate within and between these hosts in order to colonize peripheral tissues for disease development in the humans. Accordingly, periplasmic flagellar motility is reported to be crucial for the infectious life cycle of B. burgdorferi. Howevr, knowledge about the spirochetes asynchronous mode of motility, flagellar motor assembly, or why or how the periplasmic flagella orient toward the cell body, not to the cell poles, is limited. Comparing the spirochetes' periplasmic flagellar motors with externally located flagellar motors, such as those seen in Escherichia coli, indicates that while many of those structures are similar, there are a few motor structures that are unique to the spirochetes. One such example is the collar structure detected by cryo-electron tomography (Cryo-ET). This structure is found only in the spirochetes, yet nothing is known about the proteins encoding the collar or their function in any spirochete. Because of its enormous structural size and central location in the motor, we hypothesize that the collar structure is comprised of multiple proteins which are important for flagellar assembly, the spirochete's distinctive wave-like morphology, normal orientation of periplasmic flagella, and motor rotation, i.e. motility. Our goal is to understand the spirochetes distinctive asynchronous motility and assembly of flagellar motors in B. burgdorferi, which we believe, can serve as a model to understand the structure and function of flagellar motors in other medically important yet uncultivable spirochetal pathogens, such as Treponema pallidum as well as other significant spirochetes. Two specific Aims are proposed to address our hypotheses. In Specific Aim 1, we propose to identify proteins encoding the unique collar structure using bioinformatics, co-immunoprecipitation, or pull-down assays followed by mutagenesis and cryo-ET analyses. Using some of these protocols we have already discovered three novel flagellar proteins. Specific Aim 2 will determine the location and structure of each flagellar component in the motor. Moreover, interaction between the collar and other key flagellar proteins is predicted to be crucial for stability or motor assembly, which will be addressed using protein-protein interaction assays. Together, this proposal intends to identify the collar motor proteins and elucidate their contribution to the spirochete's wave-like morphology, unique asymmetric motility, and flagellar orientation in B. burgdorferi. Because the collar proteins are predicted to be crucial for motility and motility for virulence (by several species of spirochetes), this project has the potential to lead to the development of a pharmacological agent aimed at blocking motility, and thereby preventing the spread of Lyme as well as other spirochete-borne diseases.